On Sat, 23 Feb 2013 17:07:31 -0800, "Sal" salmonella@food
poisoning.org wrote:


"Jeff Liebermann" wrote in message
.. .
On Fri, 15 Feb 2013 23:31:52 -0800, "Sal" salmonella@food
poisoning.org wrote:

I'm building a yagi from the measurement tables the ARRL Antenna Book.

Which Antenna Book and which yagi?

snip

Jeff, I have the 18th Edition of the ARRL Antenna Book, copyright 1997.
I'm in Chapter 18, titled "VHF and UHF Antenna Systems." I'm using Table
16, titled "Dimensions for 16-element 3.9-wavelength 222-MHz Yagi."

I have the 19th edition. Same table on Pg 18-31.

I'm bugged by something else I'm seeing. Table 16 specifies a 664 mm driven
element (DE) It's longer than the DE of other construction articles. Most
articles call for something between 645 and 648 mm. (Example: On the same
page as Table 16, I see also Table 14, "Free-Space Dimensions for the
222-MHz Yagi Family." It gives a DE of 647 mm.)

That's easy. Both antennas have elements connected to the aluminum
boom (except for the driven element). Looks like the boom diameters
are different. When the elements are connected to the boom in this
manner, the boom becomes part of the element in that the conduction
path now goes around the boom. This tends to shorten the element
lengths. All the various yagi designer programs can include the boom
diameter in their calculations. I strongly suggest that unless you're
building EXACTLY what's in the article, that you use one of the
programs previous mentioned to grind the numbers correctly.

In addition, I have a suggestion. If you're using a solid rod for the
elements, round off the ends to a hemispherical radius. Use 1/2 the
distance between the base of the radius and the peak for the element
end point. If you're using hollow tubing, you can also cram a big
rivet or screw into the end to get the same rounded effect. This will
increase your usable bandwidth.

Something is indisputably okay. My prototype DE (664 mm) is hanging by
strings above my bench and I'm getting a 1.2:1 - 1.3:1 with a short length
of cable. I can hit a repeater 15 miles away with one watt without even
turning my DE vertical. Too bad neither of my analyzers works at 222.

Please note that you also get 1:1 with a dummy load. You can also
match just about anything with your gamma match. Tune the antenna for
gain, bandwidth, and/or F/B ratio. VSWR is easy to fix.

Also VSWR is not as important as pattern and gain. You can get
perfect VSWR, and have the signal sprayed all over the place. If you
look at the antenna patterns on the same pages as the tables, you'll
see that even with a properly designed antenna, you have a rather
strange and skewed pattern. Incidentally, T-match and balun should
fix the funny pattern.

Yes, I fully expect the match to need adjusting after I add parasitic
elements. The road from here-to-there has so many branches!

Not really. The first 4 or 5 elements are what provides the VSWR. Try
waving additional elements around the front of the antenna notice how
little the VSWR changes. However, the gain, directivity, and F/B
ratio certainly will be affected.

As for your lack of an antenna analyzer, this is actually a good
thing. What you really want to do is see what the antenna is doing
over a wide range of frequencies. For that, I suggest a return loss
bridge. I use a Telonic Rho-tector Model TRB-50 and a Texscan RCB-3.
Here's what's inside:
http://www.qsl.net/n9zia/rlb/texscan.png
Both will go from 0.5MHz to 1GHz. All you need is a decent RF sweep
generator, oscilloscope, terminators, and cables. You can see the
VSWR curve over the frequency range while you're tuning. You can also
do the same thing with a directional coupler and a diode detector, but
I think the return loss bridge is easier. I've also built a few for
microwave frequencies (2.4 and 5.7GHz).



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2/23/2013 9:33 PM, Jeff Liebermann wrote:
On Sat, 23 Feb 2013 17:07:31 -0800, "Sal" salmonella@food
poisoning.org wrote:


"Jeff Liebermann" wrote in message
...
On Fri, 15 Feb 2013 23:31:52 -0800, "Sal" salmonella@food
poisoning.org wrote:

I'm building a yagi from the measurement tables the ARRL Antenna Book.

Which Antenna Book and which yagi?

snip

Jeff, I have the 18th Edition of the ARRL Antenna Book, copyright 1997.
I'm in Chapter 18, titled "VHF and UHF Antenna Systems." I'm using Table
16, titled "Dimensions for 16-element 3.9-wavelength 222-MHz Yagi."

I have the 19th edition. Same table on Pg 18-31.

I'm bugged by something else I'm seeing. Table 16 specifies a 664 mm driven
element (DE) It's longer than the DE of other construction articles. Most
articles call for something between 645 and 648 mm. (Example: On the same
page as Table 16, I see also Table 14, "Free-Space Dimensions for the
222-MHz Yagi Family." It gives a DE of 647 mm.)

That's easy. Both antennas have elements connected to the aluminum
boom (except for the driven element). Looks like the boom diameters
are different. When the elements are connected to the boom in this
manner, the boom becomes part of the element in that the conduction
path now goes around the boom. This tends to shorten the element
lengths. All the various yagi designer programs can include the boom
diameter in their calculations. I strongly suggest that unless you're
building EXACTLY what's in the article, that you use one of the
programs previous mentioned to grind the numbers correctly.

In addition, I have a suggestion. If you're using a solid rod for the
elements, round off the ends to a hemispherical radius. Use 1/2 the
distance between the base of the radius and the peak for the element
end point. If you're using hollow tubing, you can also cram a big
rivet or screw into the end to get the same rounded effect. This will
increase your usable bandwidth.

Something is indisputably okay. My prototype DE (664 mm) is hanging by
strings above my bench and I'm getting a 1.2:1 - 1.3:1 with a short length
of cable. I can hit a repeater 15 miles away with one watt without even
turning my DE vertical. Too bad neither of my analyzers works at 222.

Please note that you also get 1:1 with a dummy load. You can also
match just about anything with your gamma match. Tune the antenna for
gain, bandwidth, and/or F/B ratio. VSWR is easy to fix.

Also VSWR is not as important as pattern and gain. You can get
perfect VSWR, and have the signal sprayed all over the place. If you
look at the antenna patterns on the same pages as the tables, you'll
see that even with a properly designed antenna, you have a rather
strange and skewed pattern. Incidentally, T-match and balun should
fix the funny pattern.

Yes, I fully expect the match to need adjusting after I add parasitic
elements. The road from here-to-there has so many branches!

Not really. The first 4 or 5 elements are what provides the VSWR. Try
waving additional elements around the front of the antenna notice how
little the VSWR changes. However, the gain, directivity, and F/B
ratio certainly will be affected.

As for your lack of an antenna analyzer, this is actually a good
thing. What you really want to do is see what the antenna is doing
over a wide range of frequencies. For that, I suggest a return loss
bridge. I use a Telonic Rho-tector Model TRB-50 and a Texscan RCB-3.
Here's what's inside:
http://www.qsl.net/n9zia/rlb/texscan.png
Both will go from 0.5MHz to 1GHz. All you need is a decent RF sweep
generator, oscilloscope, terminators, and cables. You can see the
VSWR curve over the frequency range while you're tuning. You can also
do the same thing with a directional coupler and a diode detector, but
I think the return loss bridge is easier. I've also built a few for
microwave frequencies (2.4 and 5.7GHz).




One thing to remember is you generally do not want elements that are
electrically connected to the boom. The connection is usually not very
good and eventually corrodes. This makes the antenna detune in an
unpredictable manner.

That said, you can weld elements to the boom, which works.

You are better off using insulated elements with inserts in the boom
holes such as Delrin.

This will change the correction factor, but that is a known.

tom
K0TAR

"tom" wrote in message
. ..

snip

One thing to remember is you generally do not want elements that are
electrically connected to the boom. The connection is usually not very
good and eventually corrodes. This makes the antenna detune in an
unpredictable manner.

That said, you can weld elements to the boom, which works.

You are better off using insulated elements with inserts in the boom holes
such as Delrin.

This will change the correction factor, but that is a known.

tom
K0TAR


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're still up
there.

If I were to continue in that vein, I could weld (torch solder, really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)

On 2/23/2013 11:41 PM, Sal wrote:


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're still up
there.

If I were to continue in that vein, I could weld (torch solder, really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)



A good source is VE7BQH, Lionel. He has a lot of info related to EME
antennas that are as well engineered as possible for obvious reasons.

I've never looked at his correction factors as I have ones for through
the boom insulated that I know work for my build type. My corrections
are from WB0TEM.

What bands are you building for?

Here's a link to some of Lionel's information at SM2CEW. If you need to
correspond with him, contact me directly and I'll get you his email.

http://www.sm2cew.com/gt.htm

tom
K0TAR

On 2/24/2013 8:43 PM, tom wrote:
On 2/23/2013 11:41 PM, Sal wrote:


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're
still up
there.

If I were to continue in that vein, I could weld (torch solder,
really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)



A good source is VE7BQH, Lionel. He has a lot of info related to EME
antennas that are as well engineered as possible for obvious reasons.

I've never looked at his correction factors as I have ones for through
the boom insulated that I know work for my build type. My corrections
are from WB0TEM.

What bands are you building for?

Here's a link to some of Lionel's information at SM2CEW. If you need to
correspond with him, contact me directly and I'll get you his email.

http://www.sm2cew.com/gt.htm

tom
K0TAR


I've done some searching for corrections for through the boom
uninsulated and found that the opinion is that it's not a good idea.
And it makes sense if you read why - the current is really high at the
center of the element and any variation in contact resistance to the
boom or material will change the result.

What you would like is the result to be based on only the insulated
element conductance and the shielding of the boom, which is easier to
calculate and less variable.

tom
K0TAR

On 2/24/2013 9:13 PM, tom wrote:
I've done some searching for corrections for through the boom
uninsulated and found that the opinion is that it's not a good idea. And
it makes sense if you read why - the current is really high at the
center of the element and any variation in contact resistance to the
boom or material will change the result.

What you would like is the result to be based on only the insulated
element conductance and the shielding of the boom, which is easier to
calculate and less variable.

tom
K0TAR


Here's a reference that mentions reasons for not using uninsulated
through the boom connectio9ns. And has some nice graphs on insulated
through the boom.

http://g7rau.demon.co.uk/sm5bsz/antennas/sa/others.htm

tom
K0TAR

"tom" wrote in message
. ..
On 2/24/2013 9:13 PM, tom wrote:
I've done some searching for corrections for through the boom
uninsulated and found that the opinion is that it's not a good idea. And
it makes sense if you read why - the current is really high at the
center of the element and any variation in contact resistance to the
boom or material will change the result.

What you would like is the result to be based on only the insulated
element conductance and the shielding of the boom, which is easier to
calculate and less variable.

tom
K0TAR


Here's a reference that mentions reasons for not using uninsulated through
the boom connectio9ns. And has some nice graphs on insulated through the
boom.

http://g7rau.demon.co.uk/sm5bsz/antennas/sa/others.htm

tom
K0TAR



OK, I'm convinced. What I need is some lightweight non-metallic material
for the
boom and I can build with the numbers I have for element lengths. I'll hit
the stores
in the morning.

I'll try a T-match, too.

"Sal"

"tom" wrote in message
. ..
On 2/23/2013 11:41 PM, Sal wrote:

snip


What bands are you building for?

Here's a link to some of Lionel's information at SM2CEW. If you need to
correspond with him, contact me directly and I'll get you his email.

http://www.sm2cew.com/gt.htm

tom
K0TAR


BANDS: This is a 220 beam intended for roof mount on my
daughter/son-in-law's house in Livermore CA to see if we can hit the Condor
Connection, which is all on 220. I'm in San Diego, with a nearby Condor
machine. My newly-licensed son-in-law thinks it would be a hoot if we could
talk directly, home-to-home. (I don't want to encourage him to buy an HF
rig for possible use on 10m, since fickle propagation has the potential to
be a buzz kill for a new ham. Upgrade to General is an unknown. He's not
ready for IRLP.)

Condor has two possible repeaters, one on Mount Hamilton (24 mi, by San
Jose) and one on Mount Vaca (50 mi.). Neither is a slam dunk from Livermore
because of terrain blockage. I'm hoping 50W & 10 dB gain will work. I did
some Longley Rice modeling here

http://lrcov.crc.ca/main/ and I'm hopeful.

I have alternate possibilities. The WIN System has 440-band repeaters on Mt
Oso (25 mi.) and on Loma Prieta (40 mi.) but also with terrain issues. ( I
already have a 26-element 440 beam; it models out to about 14 dBd gain.)

Those distances would be no problem except for the blockage. I can do 80
miles with 5 watts off an omni if my RF's don't bump into nuthin' first.

I expect the finished 220 beam to have about 10dBd gain and I have 50 watts
available.

Thanks for the link to Lionel's info. I'll check itout.

"Sal"
(KD6VKW)

On 2/25/2013 12:38 AM, Sal wrote:

BANDS: This is a 220 beam intended for roof mount on my
daughter/son-in-law's house in Livermore CA to see if we can hit the Condor
Connection, which is all on 220. I'm in San Diego, with a nearby Condor
machine. My newly-licensed son-in-law thinks it would be a hoot if we could
talk directly, home-to-home. (I don't want to encourage him to buy an HF
rig for possible use on 10m, since fickle propagation has the potential to
be a buzz kill for a new ham. Upgrade to General is an unknown. He's not
ready for IRLP.)

Condor has two possible repeaters, one on Mount Hamilton (24 mi, by San
Jose) and one on Mount Vaca (50 mi.). Neither is a slam dunk from Livermore
because of terrain blockage. I'm hoping 50W & 10 dB gain will work. I did
some Longley Rice modeling here

http://lrcov.crc.ca/main/ and I'm hopeful.

I have alternate possibilities. The WIN System has 440-band repeaters on Mt
Oso (25 mi.) and on Loma Prieta (40 mi.) but also with terrain issues. ( I
already have a 26-element 440 beam; it models out to about 14 dBd gain.)

Those distances would be no problem except for the blockage. I can do 80
miles with 5 watts off an omni if my RF's don't bump into nuthin' first.

I expect the finished 220 beam to have about 10dBd gain and I have 50 watts
available.

Thanks for the link to Lionel's info. I'll check itout.

"Sal"
(KD6VKW)



Sounds like a plan. Good luck.

If there are any 6m machines around the terrain becomes a lot less of a
problem. If, of course, you have a 6m FM rig. Around here, Minneapolis
metro, we have a few machines that have multiple inputs and outputs.
(Not really, they are individual cross-linked rptrs, but that's just
details). Maybe your area has some.

tom
K0TAR

Sounds like a plan. Good luck.

If there are any 6m machines around the terrain becomes a lot less of a
problem. If, of course, you have a 6m FM rig. Around here, Minneapolis
metro, we have a few machines that have multiple inputs and outputs. (Not
really, they are individual cross-linked rptrs, but that's just details).
Maybe your area has some.

tom
K0TAR

Thanks. I've heard 6m is very good that way. I have 6m FM but not my
son-in-law ... yet. Besides, I haven't found any linking from Livermore to
me in Southern CA.

See, Livermore has plenty of repeaters, both local and in three nearby
cities, Tracy, Pleasanton and Danville. Once you get beyond that region,
mountains become an issue and the nearest known linked repeaters are not
line-of-sight. I'm hoping some antenna gain will let me use edge
diffraction to make one of the machines. I'm hoping the first edge out of
Livermore will do it. Yes, I have consulted terrain profiles.

Related: At Lowes today, I bought an 8-foot length of stiff, ribbed,
plastic channel called "lattice moulding" and it will be the boom for my
1.25m masterwork. It's very rigid in the vertical orientation, which is
what I want. If I have time, I'll rebuild the driven element with a
T-match.

"Sal"